1. Field of the Invention
This invention relates to a communication terminal equipped with a press-to-talk switch.
2. Description of the Prior Art
Communication services for transmitting information by various means have recently been made available owing to marked progress in mobile radio communication. For instance, a communication terminal equipped with a press-to-talk switch enables an operator to receive a communication service from a base station or other station by selecting a desired channel in order to acquire various information on a real-time basis and press the press-to-talk switch only when he/she requests transmission. Therefore, this is very convenient especially when the operator is engaged in complicated operation or carrying the terminal.
FIG. 9 is a block diagram of a communication terminal B of the prior art. In FIG. 9, reference numeral 1 is a press-to-talk switch which is pressed or released by the operator, 2 a receiver for controlling a speaker 4, 3 a transmitter for controlling a microphone 5, 6 a press-to-talk switch detection unit for detecting whether the press-to-talk switch 1 is pressed or not, 7 a communication control unit for controlling the receiver 2 and the transmitter 3 in accordance with detection information from the press-to-talk switch detection unit 6 and information from a base station 8, 8 the base station for providing a communication service to the communication terminal B, and 9 channels between the base station 8 and the communication terminal B. The press-to-talk switch 1, receiver 2, transmitter 3, speaker 4, microphone 5, press-to-talk switch detection unit 6 and communication control unit 7 are provided within the communication terminal B.
A description is given of the operation of the communication terminal B of the prior art. When the communication terminal B receives a communication service from the base station 8, the communication control unit 7 activates the receiver 2 to receive signals from the base station over a channel 9. Thereby, a voice from the base station 8 is received and output from the speaker 4. When the communication terminal B requests transmission over a channel 9, the operator presses the press-to-talk switch 1, and the press-to-talk switch detection unit 6 detects it and informs the communication control unit 7 of it. Thereby, the communication control unit 7 activates the transmitter 3 and stops the operation of the receiver 2. At the same time, the communication control unit 7 carries out processing for transmission to the base station 8. Thereby, the output of a voice from the base station 8 through the speaker 4 is stopped and a voice from the microphone 5 is transmitted and output to the base station 8. When the operator stops pressing the press-to-talk switch 1 to release the press-to-talk switch 1, the press-to-talk switch detection unit 6 detects it and informs the communication control unit 7 of it. Thereby, the communication control unit 7 stops the operation of the transmitter 3 and re-activates the receiver 2. At the same time, the communication control unit 7 carries out processing for the termination of transmission to the base station 8. Thereby, a voice from the base station 8 is received and output from the speaker 4 again. Thus, the communication terminal B of the prior art is switched between transmission and reception each time the press-to-talk switch 1 is pressed and released. The press-to-talk switch l must be kept pressed while transmission is continued.
FIG. 10 is a flow chart showing operation procedure from the selection of a desired channel by the communication terminal B of the prior art to the disconnection of the channel. With reference to FIG. 10, complicated operation when a plurality of channels are used will be described. The operator first selects a desired one from the plurality of channels and sets it in the communication terminal B (see step 501). The channel number inputting function and scanning function of the communication terminal B are used to select and set the desired channel in the communication terminal B. This is a first operation. When the operator requests to connect his/her own communication terminal B to his/her desired channel in this state, he/she presses the press-to-talk switch 1 (see steps 502 and 503). Thereby, the communication terminal B carries out the connection of the channel. When the press-to-talk switch 1 is kept pressed after the connection, the communication terminal B is switched to transmission (steps 504 and 505). These are second and third operations.
On the other hand, to receive signals by connecting a desired channel, the operator selects his/her desired channel and waits for signals from the base station 8 over the channel (see steps 501 and 506). After the reception of the signals, the communication terminal B is connected to the channel. Thereby, the communication terminal B is switched to reception (see step 508). When the operator wants to transmit signals, he/she keeps pressing the press-to-talk switch 1 to switch the communication terminal B from reception to transmission so that transmission can be continued (see steps 509, 504 and 505). This is also a second operation. When the operator wants to terminate transmission and return to reception in this state, he/she releases the press-to-talk switch 1 to switch the communication terminal B from transmission to reception. Thus, transmission is terminated and reception is resumed (see steps 504 and 508). This is a fourth or third operation after transmission. Thereafter, when the operator wants to terminate communication or select another desired channel by disconnecting the connected channel, he/she makes a channel connection request. Thereby, the communication terminal B returns to the initial channel selection state (see steps 509 and 501). Thus, the communication terminal B of the prior art requires several operations such as pressing, keeping pressing and releasing of the press-to-talk switch 1 for the process from the selection of a desired channel to the disconnection of the channel. The same operations are required especially for emergency communication.
The case where the communication terminal of the prior art receive signals from an old channel and cannot select a new channel when the operator wants to select the new channel after the disconnection of the old channel will be described with reference to FIG. 10. When the currently connected channel is to be disconnected and a new channel is to be selected, the currently connected channel is selected in the communication terminal B as shown in steps 509 and 501. In this state, the operator operates the communication terminal B to select a new channel. However, as described above, the state where the communication terminal B selects a channel is also a state where the communication terminal waits for reception as shown in steps 501 and 506. Therefore, when the communication terminal B receives signals from the base station 8 over the connected channel, the communication terminal B is connected to the channel. Therefore, the operation of selecting a new channel is interrupted and the communication terminal B is switched to reception. In the communication terminal B of the prior art, the selection of a channel is interrupted to improve the connection rate of channels and a channel cannot be selected freely, resulting in complicated operation.
The communication terminal B equipped with the press-to-talk switch 1 of the prior art requires several operations of the press-to-talk switch 1 for the process from the selection of a desired channel to the disconnection of the channel and for the selection of a new channel after the connection of a channel as described above. In addition, these operations are complicated. Therefore, when the communication terminal B is used while the operator is engaged in complicated operation or carrying it, its operation is complicated.